Evaluation of the quality of electrode contact with a skin surface

ABSTRACT

An instrument that utilizes body contact electrodes evaluates the quality of the connections made between the electrodes and the body. An electrode contact quality evaluation circuit performs the quality evaluation, such as by determining contact impedances for the electrodes. The corresponding contact quality of each electrode is conveyed to the user.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/624,645 filed on Sep. 21, 2012 and entitled EVALUATION OF THE QUALITYOF ELECTRODE CONTACT WITH A SKIN SURFACE, the disclosure of which ishereby incorporated by reference in its entirety.

BACKGROUND

There are a variety of instruments that are designed to interact with apatient through electrodes applied to the patient's skin. Severalexamples include electrocardiograph (ECG), electroencephalograph (EEG),and electromyograph (EMG) instruments. Such instruments operate bymaking electrical connections with the skin, through which electricalsignals can pass.

The quality of the contact between the electrode and the skin cangreatly impact the quality of the signal obtained from the patient.Several factors can influence the quality of the connection. A majorfactor is whether appropriate skin preparation steps are taken prior tothe connection of the electrode. A skin preparation process may includeshaving the skin surface to remove hairs, cleaning the skin surface, andlightly abrading the skin surface to remove dead skin cells. Theelectrode itself can also influence the quality of the connection. Forexample, some types of electrodes can become dried out over time. Theelectrical connection quality can also be reduced if a conductive gel isnot applied between the skin and certain types of electrodes thatrequire such a gel. If a non-conductive gel, such as a type used forultrasound procedures, is inadvertently used, the quality of theelectrical connection can be reduced.

Even if electrodes appear to be well connected to the skin and skinpreparation has been properly done, the quality of the electricalcontact can still be relatively poor for some patients. A visual orphysical inspection of the electrodes is not adequate to determine thequality of the connection. A poor electrical connection can result inincreased susceptibility to interference, or complete inability of theinstrument to interact with the patient in the intended manner.

SUMMARY

In general terms, this disclosure is directed to systems and methods forevaluating the quality of electrode contact with a skin surface.

One aspect is an instrument comprising: a lead interface deviceconfigured to electrically communicate with at least three surfacecontact electrodes; instrument electronics configured to detectelectrical signals from the surface contact electrodes; and electrodecontact quality evaluation circuitry operable to determine a quality ofelectrical connections between the surface contact electrodes and a skinsurface.

Another aspect is an electrode contact quality evaluation deviceconfigured to evaluate a connection between at least one electrode and askin surface, the electrode contact quality evaluation devicecomprising: a current source that generates a test current; an injectionelectrode selection circuit that supplies the test current to a selectedinjection electrode through a selected injection lead; a driven returncircuit that generates a return current having opposite polarity to thetest current; a return electrode selection circuit that supplies thereturn current to a selected return electrode through a selected returnlead; a sense electrode selection circuit that supplies a signalobtained from one or more selected sense electrodes through one or moreselected sense leads, to the driven return circuit; differentialmeasurement circuitry that measures differences between signals presentat the injection lead and the one or more sense leads and betweensignals present at the one or more sense leads and the return lead; anda processing device that evaluates the differences and generates anoutput representing a quality of at least one connection between atleast one of the electrodes and the skin surface.

A further aspect is an electrocardiograph comprising: a base unitcomprising: a housing; a computing device at least partially containedwithin the housing; and an output device at least partially containedwithin the housing and configured to output information associated withelectrical signals from the heart of a patient detected by theelectrocardiograph; a lead interface unit having a lead interfacehousing separate from the housing of the base unit, the lead interfaceunit comprising: a lead interface arranged and configured to physicallyconnect the lead interface unit to electrically conductive leads,wherein the leads are configured to be physically connected to surfacecontact electrodes; electrode contact detection circuitry within thelead interface housing that detects contact between the surface contactelectrodes and the patient; electrode contact quality evaluationcircuitry within the lead interface housing, wherein the electrodecontact quality evaluation circuitry determines a quality of electricalconnections between the surface contact electrodes and the patient; andinstrument electronics within the lead interface housing that detectelectrical signals from the heart of the patient; and a communicationinterface between the lead interface unit and the base unit.

Yet another aspect is a method of evaluating the quality of electrodecontact with a skin surface, the method comprising: checking for anddetermining that at least three electrodes are in physical contact witha skin surface using electrode contact detection circuitry; andevaluating and determine a quality of an electrical connection betweenat least one of the electrodes and the skin surface using electrodecontact quality evaluation circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example instrument that interactswith a patient through surface contact electrodes.

FIG. 2 is a perspective view of an example base unit of the instrumentshown in FIG. 1.

FIG. 3 is a schematic block diagram of the base unit shown in FIG. 2.

FIG. 4 illustrates an exemplary architecture of a computing device ofthe base unit shown in FIG. 2.

FIG. 5 illustrates several components of the example instrument shown inFIG. 1, including a cable, a lead interface unit, and leads.

FIG. 6 is a side view illustrating an example clip and an exampleelectrode applied to the skin of a patient.

FIG. 7 is a functional block diagram of an example of the lead interfaceunit shown in FIG. 5.

FIG. 8 is a schematic block diagram illustrating an example hardwareconfiguration of the lead interface unit shown in FIG. 5.

FIG. 9 is a schematic diagram illustrating an example of electrodecontact quality evaluation circuitry and its interfaces to the patient.

FIG. 10 illustrates a simplified schematic example of driven returncircuitry of the electrode contact quality evaluation circuitry shown inFIG. 9.

FIG. 11 is a flow chart illustrating an example method of operating aninstrument using surface contact electrodes.

FIG. 12 is a flow chart illustrating an example method of determiningelectrode contact impedances.

FIG. 13 is a flow chart illustrating an example method of determining anelectrode contact quality level.

FIG. 14 is a flow chart illustrating an example method of generating avisual indication of an electrode contact quality level.

FIG. 15 is a diagram illustrating an example display showing theelectrode contact quality levels.

DETAILED DESCRIPTION

Various embodiments will be described in detail with reference to thedrawings, wherein like reference numerals represent like parts andassemblies throughout the several views. Reference to variousembodiments does not limit the scope of the claims attached hereto.Additionally, any examples set forth in this specification are notintended to be limiting and merely set forth some of the many possibleembodiments for the appended claims.

FIG. 1 is a perspective view of an example instrument 100 that interactswith a patient through skin contact electrodes. The instrument 100 cantake various forms in a variety of possible embodiments. Severalexamples of the instrument 100 include an electrocardiograph (ECG), anelectroencephalograph (EEG), and an electromyograph (EMG) instrument.The following description makes reference to an example embodimentinvolving an electrocardiograph instrument 100, but it is recognizedthat other embodiments include other instruments in which skin contactelectrodes are used to interact with a patient.

In this example, the instrument 100 is a mobile electrocardiographinstrument that includes a base unit 102, a cart 104, a cable 106, alead interface unit 108, leads 110, and electrodes 112. The electricalcomponents of the instrument 100 are contained within the base unit 102and the lead interface unit 108. The cart 104 provides a mobile platformthat supports the base unit 102. The cable 106 and leads 110 includeelectrical conductors which conduct electrical signals between the baseunit 102, the lead interface unit 108, and the electrodes 112. Theelectrodes 112 are connected to the skin S of the patient P.

The electrocardiograph instrument 100 utilizes the electronics withinthe base unit 102 and the lead interface unit 108 to detect andinterpret electrical signals from the heart of the patient P. Theelectrical signals are recorded by the electrocardiograph instrument 100in a computer readable storage device, and can be output in a variety ofmanners, including by printing the electrical signals on paper,displaying the electrical signals on a display, or transferring digitaldata representing the electrical signals to another device, such asacross a data communication network. Examples of the base unit 102 andthe lead interface unit 108 are illustrated and described in more detailherein.

The instrument 100 also includes electrode contact quality evaluationcircuitry 120, which operates to evaluate the quality of the contactbetween the electrodes and skin of the patient P. In some embodimentsthe electrode contact quality evaluation circuitry 120 is part of thelead interface unit 108, as shown in FIG. 1, while in other embodimentsthe circuitry 120 is part of the base unit 102, or a combination of thebase unit 102 and the lead interface unit 108. One or more different oradditional units may also be included in some embodiments, which mayalternatively include some or all of the circuitry 120. An example ofthe electrode contact quality evaluation circuitry 120 is illustratedand described in more detail with reference to FIGS. 7-15.

A cable 106 transfers electrical signals between the lead interface unit108 and the base unit 102, in some embodiments. An example of the cable106 is illustrated and described in more detail with reference to FIG.5. The cable 106 is an example of a communication interface. In otherpossible embodiments, the communication interface is a wirelessinterface used to transfer digital data between the lead interface unit108 and the base unit 102.

Leads 110 each include one or more insulated conductors that transferelectrical signals between the lead interface unit 108 and individualelectrodes 112. Typically the instrument 100 includes at least threeleads 110, and more typically includes a larger number of leads, such as5, 10, or more. An example is described herein that includes 10 leads.The leads 110 are illustrated and described in more detail herein withreference to FIG. 5.

Electrodes 112 are electrically conductive devices that are configuredto be placed on and connected to the surface of the skin S of thepatient P. A wide variety of electrodes 112 can be used, includingreusable and disposable electrodes. Some electrodes 112 include anadhesive layer for fastening to the skin, while other embodiments useother fasteners, such as a suction-cup type of device. The electricalcontact and suction seal of some electrodes can be improved by placingan electrically conductive gel, paste, or creme between the electrode112 and the skin S. Appropriate skin preparation steps can also be usedto improve the electrical contact between the electrodes 112 and theskin. These steps can include shaving, cleansing, and lightly abrading.

Electrodes 112 are typically placed in precise locations on the patientP during electrocardiography. The individual electrodes 112 can bereferred to by their locations. Examples of common electrode locationsinclude: V1 (fourth intercostal space at right sternal border), V2(fourth intercostal space at left sternal border), V3 (midway between V2and V4), V4 (fifth intercostal space at the left midclavicular line), V5(anterior axillary line at the same horizontal level as V4), V6(mid-axillary line on the same horizontal level as V4 and V5), LA (leftarm—just above the left wrist on inside of arm), LL (left leg—just abovethe left ankle), RL (right leg—just above the right ankle), RA (rightarm—just above the right wrist on inside of arm). Other electrodearrangements are used at other times or with other embodiments. Forexample, a different arrangement may be used with small children.

FIGS. 2 and 3 illustrate an example of the base unit 102, shown inFIG. 1. FIG. 2 is a perspective view of the base unit 102 and FIG. 3 isa schematic block diagram of the base unit 102. In this example, thebase unit 102 includes a housing 130, a display device 132, an inputinterface 134, a printer 136, a computing device 140, a power supply142, a communication interface 144, and a network interface 146.

The housing 130 provides a protective enclosure for base unitelectronics contained therein.

The display device 132 is a device that generates a visual userinterface to convey information to a user, such as a clinician. Examplesof displays 132 include liquid crystal displays, light emitting diode(LED) displays, and the like.

The input interface 134 operates to receive input from a user, such asthrough a plurality of selectable buttons. The buttons can be arrangedin a keyboard configuration, and can include additional controls forselecting options presented on the display device 132. One or moreswitches can be used to detect user-inputs in some embodiments. Theinput interface 134 can include a variety of other possible devices inother embodiments, such as a microphone for receiving voice commands, awireless interface for receiving input through a wireless device, suchas a remote control or keypad, a network communication device forreceiving inputs from or sending data to a remote device, etc.

The printer 136 prints reports related to the electrocardiogram. In someembodiments the printer 136 prints reports that graphically depict oneor more electrical signals that were detected from the patient's heart.

The computing device 140 includes at least a processing device and atleast one computer readable storage device. The processing deviceoperates to execute data instructions stored in the computer readablestorage device to perform various operations, methods, or functionsdescribed herein. An example of the computing device 140 is illustratedand described in more detail with reference to FIG. 4.

The power supply 142 typically receives power from an external source,such as through a power cord that can be connected to a wall receptacle.In some embodiments the power supply includes an alternating current(AC) to direct current (DC) converter, as well as various filtering andsurge protection circuitry, and supplies power at a suitable level toelectronics contained within the housing 130, as well as to the leadinterface unit 108 through cable 106. Other possible embodiments includeother power sources, such as a battery power supply.

The communication interface 144 includes circuitry to communicate withthe lead interface unit 108, such as through cable 106. In anotherpossible embodiment, the communication interface 144 includes a wirelessreceiver, or transceiver for communicating wirelessly with the leadinterface unit 108.

The network interface 146 includes a network communication device thatoperates to communicate digital data across a data communication network150. An example of the network interface 146 is an Ethernet networkinterface device having an Ethernet port for receiving an Ethernet cableand transmitting and receiving digital data across the Ethernet cable toa network 150 such as a local area network or the Internet. In otherpossible embodiments, the network interface 146 includes one or more ofa wireless communication device such as a cellular communication device,a Wi-Fi communication device (such as conforming to one of the IEEE802.11 family of communication protocols), a Bluetooth® communicationdevice, and the like. In some embodiments the network interface 146 is apart of the computing device 140, as illustrated in FIG. 4.

FIG. 4 illustrates an exemplary architecture of a computing device thatcan be used to implement aspects of the present disclosure, includingthe computing device 140 of the base unit 102. The computing deviceillustrated in FIG. 4 can be used to execute any one or more of theoperating system, application programs, software modules, and softwareengines, as described herein. By way of example, the computing devicewill be described below as computing device 140 of the base unit,although additional computing devices can be included in someembodiments, such as one or more computing devices that are in datacommunication with the computing device 140 across data communicationnetwork 150. To avoid undue repetition, this description of thecomputing device will not be separately repeated herein for each of theother possible computing devices, but such devices can also beconfigured as illustrated and described with reference to FIG. 4.

The computing device 140 includes, in some embodiments, at least oneprocessing device 180, such as a central processing unit (CPU). Avariety of processing devices are available from a variety ofmanufacturers, for example, Intel or Advanced Micro Devices (AMD). Inthis example, the computing device 140 also includes a system memory182, and a system bus 184 that couples various system componentsincluding the system memory 182 to the processing device 180. The systembus 184 is one of any number of types of bus structures including amemory bus; a peripheral bus; and a local bus using any of a variety ofbus architectures.

Examples of computing devices suitable for the computing device 140include a microcontroller, a microprocessor, a desktop computer, alaptop computer, a tablet computer, a mobile computing device (such as asmart phone, an iPod® or iPad® mobile digital device, or other mobiledevices), or other devices configured to process digital instructions,although in typical embodiments the computing device 140 is a part ofthe base unit 102 (FIGS. 2-3) and does not include a separate housing.

The system memory 182 includes program memory 186 and random accessmemory 188. A basic input/output system 190 containing the basicroutines that act to transfer information within computing device 140,such as during start up, is typically stored in the program memory 186.

The computing device 140 also includes a secondary storage device 192 insome embodiments, such as a hard disk drive, for storing digital data.The secondary storage device 192 is connected to the system bus 184 by asecondary storage interface 194. The secondary storage devices 192 andtheir associated computer readable media provide nonvolatile storage ofcomputer readable instructions (including application programs andprogram modules), data structures, and other data for the computingdevice 140.

Although the exemplary environment described herein employs a hard diskdrive as a secondary storage device, other types of computer readablestorage media are used in other embodiments. Examples of these othertypes of computer readable storage media include magnetic cassettes,flash memory cards, digital video disks, Bernoulli cartridges, compactdisc memories, digital versatile disk memories, random access memories.Some embodiments include non-transitory media. Additionally, suchcomputer readable storage media can include local storage or cloud-basedstorage.

A number of program modules can be stored in secondary storage device192 or memory 182, including an operating system 196, one or moreapplication programs 198, other program modules 200 (such as thesoftware engines described herein), and program data 202. The computingdevice 140 can utilize any suitable operating system, such as MicrosoftWindows™, Google Chrome™, Apple OS, and any other operating systemsuitable for a computing device. Other examples can include Microsoft,Google, or Apple operating systems, or any other suitable operatingsystem used in tablet computing devices.

In some embodiments, a user provides inputs to the computing device 140through one or more input devices 204. Examples of input devices 204include a keyboard 206, mouse 208, microphone 210, and touch sensor 212(such as a touchpad or touch sensitive display). Other embodimentsinclude other input devices 204. The input devices are often connectedto the processing device 180 through an input interface 134 that iscoupled to the system bus 184. These input devices 204 can be connectedby any number of input/output interfaces, such as a parallel port,serial port, game port, universal serial bus, or a custom interface.Wireless communication between input devices and the interface 134 ispossible as well, and includes infrared, BLUETOOTH® wireless technology,802.11a/b/g/n, cellular, or other radio frequency communication systemsin some possible embodiments.

In this example embodiment, a display device 132, such as a monitor,liquid crystal display device, projector, or touch sensitive displaydevice, is also connected to the system bus 184 via an interface, suchas a display controller 218. In addition to the display device 132, thecomputing device 140 can control various other peripheral devices (notshown), such as a speaker or a printer.

When used in a local area networking environment or a wide areanetworking environment (such as the Internet), the computing device 140is typically connected to the network 150 through a network interface146, such as an Ethernet interface. Other possible embodiments use othercommunication devices. For example, some embodiments of the computingdevice 140 include a modem for communicating across the network 150.Wireless communication with the network 150 is also possible through awireless communication device, such as described herein.

The computing device 140 typically includes at least some form ofcomputer readable media. Computer readable media includes any availablemedia that can be accessed by the computing device 140. By way ofexample, computer readable media include computer readable storage mediaand computer readable communication media.

Computer readable storage media includes volatile and nonvolatile,removable and non-removable media implemented in any device configuredto store information such as computer readable instructions, datastructures, program modules or other data. Computer readable storagemedia includes, but is not limited to, random access memory, read onlymemory, electrically erasable programmable read only memory, flashmemory or other memory technology, compact disc read only memory,digital versatile disks or other optical storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium that can be used to store the desired informationand that can be accessed by the computing device 140.

Computer readable communication media typically embodies computerreadable instructions, data structures, program modules or other data ina modulated data signal such as a carrier wave or other transportmechanism and includes any information delivery media. The term“modulated data signal” refers to a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, computer readable communication mediaincludes wired media such as a wired network or direct-wired connection,and wireless media such as acoustic, radio frequency, infrared, andother wireless media. Combinations of any of the above are also includedwithin the scope of computer readable media.

The computing device illustrated in FIG. 4 is also an example ofprogrammable electronics, which may include one or more such computingdevices, and when multiple computing devices are included, suchcomputing devices can be coupled together with a suitable datacommunication network so as to collectively perform the variousfunctions, methods, or operations disclosed herein.

FIG. 5 illustrates various components of the example instrument 100(shown in FIG. 1), including the cable 106, the lead interface unit 108,and the leads 110.

The cable 106 includes electrical conductors enclosed in one or moreelectrically insulating layers. In this example, the cable 106 includesa plug end 230 configured to be connected to a mating port on the baseunit 102 (shown in FIG. 2). The other end 232 of the cable 106 ispermanently connected to the housing of the lead interface unit 108, inthis example. During operation, the cable 106 is connected to the matingport on the base unit 102, and the cable conducts electrical signalsbetween the lead interface unit 108 and the base unit 102.

In some embodiments the lead interface unit 108 includes a housing 240,electronic components 242 contained within the housing (and not visiblein FIG. 5), a plurality of lead interface ports 244, and an electrodeconnection display device 246. The lead interface unit 108 is typicallysized to fit within the hand of a person, and configured so that it canbe placed near to the patient during an ECG procedure. Although theelectronic components 242 can alternatively be contained within the baseunit 102, placement of the electronic components 242 within the leadinterface unit 108 reduces the necessary length of the leads 110, andimproves the quality of the signals obtained by reducing theelectromagnetic interference received by the leads.

An example of the lead interface unit 108 is illustrated and describedin more detail herein with reference to FIGS. 7-15.

In some embodiments the lead interface unit 108 includes an electrodeconnection display device 246. The electrode connection display device246 provides feedback to the user regarding the electrode connectionstatus. In some embodiments, the electrode connection display device 246indicates whether the electrodes 112 (connected to leads 110, and shownin FIGS. 1 and 6) have been connected to the patient P (shown in FIG.1). In other embodiments, the electrode connection display device 246indicates the quality of the connection between the electrode 112 andthe patient P.

In some embodiments the electrode connection display device 246 includeslights, such as light emitting diodes (LEDs) that are selectivelyilluminated by the lead interface unit 108 to convey information to theuser. In another possible embodiment, the electrode connection displaydevice 246 is a display device, such as an LCD display.

In one example embodiment, the electrode connection display device 246indicates whether the electrodes 112 are connected to the patient. Forexample, an LED emitting a first color (e.g., green) may indicate thatone of the electrodes 112 is connected, while an LED emitting a secondcolor (e.g., white), or off, may indicate that the electrode 112 is notconnected.

In another possible embodiment, the electrode connection display device246 indicates the quality of the connection between the electrode 112and the patient P. In this example, a first color (e.g., green) mayindicate a good connection, a second color (e.g., yellow) may indicate apoor connection, and a third color (e.g., red, blue, or off) mayindicate that no connection is detected.

The leads 110 include one or more electrical conductors that areenclosed in one or more electrically insulating materials. In thisexample, the leads 110 include a lead interface plug end 250 and anelectrode plug end 252. The plug end 250 includes a plug that isconfigured to be inserted within the lead interface ports 244, tophysically connect the leads 110 to the lead interface unit 108, and toelectrically connect the lead 110 conductors to the electroniccomponents 242 of the lead interface unit 108. The plug end 252 includesa plug that is configured to be inserted into a clip 260 (such as shownin FIG. 6), to physically connect the lead 110 to the clip 260, and toelectrically connect a conductor in the lead 110 to a conductor in theclip 260.

Other embodiments include other types of leads 110, which can havedifferent ends. For example, plug end 252 can alternatively include apinch clip end, a snap end, or other terminating device. In addition,either of the plug end 250 or the plug end 252 can be permanentlyconnected to the lead interface unit 108 or the electrodes 112respectively. Other terminating devices can be used in otherembodiments.

The electrodes 112 are placed at precise locations on the body, and theelectrodes 112 and corresponding leads 110 can be referred to by theselocations. In this example, the locations include: V1 (fourthintercostal space at the right sternal border), V2 (fourth intercostalspace at the left sternal border), V3 (midway between V2 and V4), V4(fifth intercostal space at the left midclavicular line), V5 (anterioraxillary line at the same horizontal level as V4), V6 (mid-axillary lineon the same horizontal level as V4 and V5), LA (left arm—just above theleft wrist on inside of arm), LL (left leg—just above the left ankle),RL (right leg—just above the right ankle), RA (right arm—just above theright wrist on inside of arm). Other electrode configurations can beused, however, in which case the leads can be referred to by thealternate positions. For example, an alternate configuration can be usedon a small child where the standard positions may be too closelypositioned.

FIG. 6 is a side view illustrating an example clip 260 and an exampleelectrode 112 applied to the skin S of a patient P.

As discussed herein, a variety of different types of electrodes 112 withvarious embodiments of instrument 100, and some instruments 100themselves can be used with various different types of electrodes 112.FIG. 6 illustrates one example including a disposable electrode 112. Thedisposable electrode includes a body 270 and a tab 272. The body 270 isformed of an insulating substrate material, such as foam or otherflexible resilient material. A conductive material is provided on askin-facing surface 276 of the body 270 to make an electrical connectionwith the skin S of the patient P. The conductive material iselectrically connected to the tab 272, which also includes a conductivematerial on at least one surface of the tab 272.

The clip 260 can be fastened to the tab 272 to make an electricalconnection with the conductive material on the tab 272. In this example,the clip 260 includes a body 282, lead connection port 284, jawactuation button 286, and jaws 288.

A lead connection port 284 is formed at one end of the body 282 toreceive a plug end 252 of one of the leads 110 (shown in FIG. 5). Whenthe plug end 252 is inserted into the lead connection port 284, the body282 makes a physical connection with the lead 110. In addition, anelectrical conductor within the body is positioned to connect with theplug end 252 to make an electrical connection with a conductor in thelead 110.

The electrical conductor of the clip 260 extends out from the body andinto the jaws 288. The jaws 288 are spring loaded in a closed position,but can be opened by depressing the jaw actuation button 286.

To connect the clip 260 to the electrode 112, the button 286 isdepressed to open the jaws 288. The jaws 288 are then arranged on eitherside of the tab 272 and the button 286 is released to cause the jaws 288to clamp onto the tab 272. The electrical conductor on the tab 272 isthen electrically connected to the electrical conductor within the jaws288. When all connections have been made as described with reference toFIGS. 5 and 6, the electrode 112 is electrically connected with the leadinterface unit 108, shown in FIG. 5.

The electrode 112 can be fastened to the skin S of the patient P in avariety of manners. In some embodiments, the skin-facing surface 276 ofthe electrode includes an adhesive layer or coating that fastens theelectrode 112 to the skin S. Some embodiments utilize one or morestraps, bands, wraps, or other fasteners to apply a force to an oppositesurface 278 of the electrode 112 to press the skin-facing surface 276against the skin S of the patient. Other fasteners or combinations offasteners can be used in other embodiments.

The quality of the electrical connection between the skin S and theskin-facing surface 276 of the electrode 112 can be greatly improved ifproper skin preparation steps are performed prior to placement of theelectrodes on the skin S. These steps typically include: shaving orclipping hair from the surface of the skin S, lightly abrading the skinwith a gauze pad or other lightly abrasive material to remove dead orloose skin, and cleansing the skin with alcohol or soap and water toremove skin oils.

In addition, electrodes 112 should be properly used and prepared. Forexample, disposable electrodes are typically provided in sealedpackages, and should be kept in the sealed packages until they are readyto be used. Disposable electrodes are often packaged with a conductivegel arranged on the skin-facing surface 276. This gel contains a desiredamount of moisture, and can become dried out if prematurely removed fromthe packaging. If removed from the packaging, the electrodes should bekept in a sealed bag to prevent or reduce evaporation. The disposableelectrodes should also be stored away from heat sources to preventdrying or other damage to the electrodes. If reusable electrodes areused, they should be cleaned and used according to manufacturerrecommendations.

If a user fails to take the appropriate skin-preparation steps, or failsto follow manufacturer's electrode storage, application, or usageguidelines, the quality of the electrical connection between theelectrode 112 and the skin S can be reduced. A poor quality connectionresults in an increased electrical contact impedance between theelectrode 112 and the patient's internal tissues beneath the skin S.

When the quality of the electrical connection between the electrode 112and the skin is reduced, the quality of signals obtained by theinstrument 100 (FIG. 1) can also be reduced, or the instrument 100 caneven be rendered entirely inoperable for the intended purpose. Forexample, the increased impedance can increase the interference caused bypower line frequencies or radio frequency noise present in theenvironment. The increased impedance can also increase artifacts indetected signals caused by physical movement of the electrodes 112 orleads 110. If the quality of the electrical connection is very low, theelectrical impedance can increase to such a level that the instrument100 is unable to obtain adequate electrical signals through theelectrodes 112, rendering the instrument inoperable for some or all ofits intended purpose(s).

Accordingly, as described herein, the instrument 100 includes electrodecontact quality evaluation circuitry 120 (shown in FIG. 1 andillustrated and described in more detail herein) that evaluates thequality of the electrical connection between each electrode 112 and theskin S. Feedback can then be provided to the user to identify thequality of each electrical connection so that the user can fix poorconnections, or the quality data can be stored or transmitted forsubsequent use. In some embodiments, the instrument 100 requires acertain level of electrode contact quality be detected before theinstrument 100 will proceed with subsequent operations.

FIG. 7 is a functional block diagram of an example lead interface unit108 according to the present disclosure. In this example, the leadinterface unit 108 includes electrode contact detection circuitry 302,electrode contact quality evaluation circuitry 120, and instrumentelectronics 306. A schematic block diagram illustrating an examplehardware configuration corresponding to the lead interface unit 108shown in FIG. 7 is illustrated and described in more detail herein withreference to FIG. 8.

The electrode contact detection circuitry 302 operates to determinewhether the electrodes 112 have been placed on the skin S of the patientP, and whether all appropriate connections have been made between theelectrodes 112 and the lead interface unit 108. In other words, in someembodiments the electrode contact detection circuitry 302 operates todetermine whether an electrical connection has been made through thelead interface unit 108 and the respective electrodes 112 to thepatient, regardless of the quality of the connection. For example, theelectrode contact detection circuitry 302 can indicate whether eachindividual electrode 112 is “connected” or “not connected.” In someembodiments, the electrode contact detection circuitry 302 applies tiny“lead fail detection” currents to each lead 110, and measures the DCvoltage component of the signal on each lead 110 with respect to thecommon (i.e. “ground”) of the floating power supply of the leadinterface unit 108. When a lead or its electrode is not connected, thatlead's dc voltage component will be far from “ground.” This isinterpreted as “not connected.” The electrode which is used as areference or return provides a path to sink the lead fail detectioncurrents through the patient's body. If the reference lead and itselectrode are connected to the patient's body, then any other electrodeand lead connection to the patient will be pulled closer to ground, andthat condition is interpreted as “connected.” This method requires atleast the reference electrode and one other electrode connection beforeany connection can be detected, i.e., the connection of no singleelectrode can be detected in this way. To facilitate detection, thechoice of reference electrode may optionally be cycled amongst each ofthe electrode possibilities until one other electrode connection is thusdetected or a fixed choice of reference electrode may be used. Allsubsequent additional electrode connections may be detected using thissame choice of reference electrode. The reference electrode itself willalways show as connected. If an alternative choice of referenceelectrode has been selected while searching for electrode contact, thepreferred choice of reference electrode may be selected after sufficientelectrodes are determined to be in contact with the patient. In someembodiments, the electrode contact detection circuitry 302 is includedwithin the instrument electronics 306.

The electrode contact quality evaluation circuitry 120 operates todetermine the quality of the connection between individual electrodes112 and the skin S of the patient P. The quality is measured as anelectrical impedance, where a higher impedance indicates a lower qualityconnection and a lower impedance indicates a higher quality connection.In some embodiments the electrode contact quality is further simplifiedby assigning the electrical impedance one of a plurality of possiblequality levels. For example, the quality may be selected from one of aplurality of quality levels, such as “unsatisfactory,” and“satisfactory.” In another embodiment, the quality levels include,“poor,” “marginal,” and “good.” Additional or different quality levelsincluding a simple ranking number are used in other embodiments.

In some embodiments, the electrode contact quality evaluation circuitrycan inhibit instrument 100 from proceeding with instrument operations(utilizing instrument electronics 306) until the electrode contactquality has been determined to meet or exceed a predetermined qualitylevel, such as at least “satisfactory” or at least “marginal,” in theexamples listed above.

The instrument electronics 306 perform the main instrument operations.For example, when the instrument is an ECG instrument, the instrumentelectronics 306 include ECG acquisition electronics to receiveelectrical signals from the heart. The ECG electronics can also performother operations, as desired for the instrument. Other instrumentsperform other operations. For example, an EEG instrument includes EEGacquisition electronics that operate to obtain electrical activity alongthe scalp of a patient. An EMG instrument includes EMG acquisitionelectronics that operate to obtain electrical activity produced byskeletal muscles. Other instruments include other instrument electronics306.

As discussed elsewhere herein, although the example shown in FIG. 7illustrates and describes the components 302, 120, and 306 withreference to an example embodiment in which the components 302, 120, and306 are part of the lead interface unit 108, in other possibleembodiments one or more of the components 302, 120, and 306 are includedas part of the base unit 102, or another portion of the instrument 100(shown in FIG. 1), as desired. Some embodiments include a shared trunkcable between the lead interface unit and the individual leads. Further,some embodiments do not include each of the components 302, 120, and306.

The lead interface unit 108 typically also includes a lead interface,best seen in FIG. 5. In some embodiments, the lead interface includes aplurality of ports 244 (which may include jacks or other receptacles,for example) that are configured to receive plug ends 250 of the leads110 to make physical and electrical connections between the leadinterface unit 108 and the leads 110. In other embodiments, the leadinterface includes a terminal block for connecting the leads 110 to thelead interface unit 108. The leads 110 can also be permanently connectedto the lead interface unit 108 in yet other embodiments.

FIG. 8 is a schematic block diagram illustrating an example hardwareconfiguration corresponding to the lead interface unit 108, shown inFIG. 7, and also illustrating leads 110, and electrodes 112.

In this example, the lead interface unit 108 includes a housing 240,electronic components 242 contained within the housing, a plurality oflead interface ports 244, and an electrode connection display device246, as shown in FIG. 5. In some embodiments, the electronic components242 include instrument electronics 306, protection circuitry 320,injection electrode selection circuitry 322, return electrode selectioncircuitry 324, sense electrode selection circuitry 326, a processingdevice 328, an input interface 330, a test current source 332, drivenreturn circuitry 334, an analog to digital converter 336, and a baseunit interface 338.

The electrodes 112 are arranged at specific locations on the skin S ofthe patient P, and are connected to the appropriate leads 110 to form anelectrical connection between the skin S and the lead interface unit108. In this example, ten electrodes are used, which are placed at thefollowing locations (which are each described in more detail herein) onthe skin S of the patient P: V1, V2 V3, V4, V5, V6, LA, LL, RL, RA.Other electrode and lead configurations and quantities are used in otherembodiments.

The leads 110 connect between the electrodes 112 and the respective leadinterface ports 244 on the housing 240 of the lead interface unit 108.

Protection circuitry 320 is provided in some embodiments, which protectsthe electronic components 242 from external electric currents, such asfrom a defibrillator. The protection circuitry 320 can include aresistor, for example, to limit current flow from the leads 110. In someembodiments the protection circuitry 320 includes a clamp circuit thatlimits the magnitude of the input signal. The clamp circuit can include,for example, a zener diode, a neon bulb, or a gas discharge tube. Someembodiments also include one or more stages of passive low pass filterbetween the clamp circuits and the rest of the circuits. These low passfilters not only reduce susceptibility to RF interference and provideadditional protection against damage from defibrillator discharges, butthe series resistor(s) in them also serve to limit the maximum currentthat can be applied through the patient during single fault conditionsof the circuitry 242.

In some embodiments the electrode contact quality evaluation circuitry120 includes electrode selection circuitry that permits the selectionbetween the various electrodes 112 to be used for different purposes. Inthis example, the electrode contact quality evaluation circuitry 120includes injection electrode selection circuitry 322, return electrodeselection circuitry 324, and sense electrode selection circuitry 326.The selection circuitry can be implemented by analog multiplexers, whichcan be controlled by the processing device to select amongst any one ofthe leads 110 and corresponding electrodes 112. Once selected, anelectrical connection is made between the selected electrode and theappropriate electronic components 242.

The instrument electronics 306 include additional electronics thatperform the one or more intended operations of the instrument 100, inaddition to the electrode contact detection circuitry 302 and theelectrode contact quality evaluation circuitry 120 (shown in FIG. 7).For example, when the instrument 100 is an ECG instrument, theinstrument electronics include ECG acquisition electronics. Otherembodiments include other instrument electronics. In some embodiments,the instrument electronics 306 may include one or more electricalcomponents that can be utilized by both of the instrument electronics306 and one or more of the electrode contact detection circuitry 302 andthe electrode contact quality evaluation circuitry 120. For example, thesense electrode selection circuitry 326 is part of the instrumentelectronics 306, and also part of the electrode contact qualityevaluation circuitry 120. However, the circuitry can be separated inother possible embodiments, if desired.

The processing device 328 performs control operations for the leadinterface unit 108. Examples of processing devices are described herein.In some embodiments, all or a portion of the electrode contact detectioncircuitry 302, electrode contact quality evaluation circuitry 120, theinstrument electronics 306 the return electrode selection circuitry 324,the driven return circuitry 334, the analog to digital converter 336,and sense electrode selection circuitry 326 may be contained in orimplemented by one or more application specific integrated circuits(“ASICs”) such as Welch Allyn's P/N 442-0016-01 or Texas Instruments'ADS1298 series parts.

The input interface 330 is provided in some embodiments to receiveinputs from a user. For example, in an embodiment in which the leadinterface unit 108 wirelessly communicates with the base unit 102, theinput interface 330 can include a “connect” button to initiate thewireless communication. Other input devices can be provided in someembodiments, such as one or more buttons, switches, touch sensitivedisplays, and other devices suitable for receiving an input from a user.Some embodiments do not include an input interface 330, and instead theinput interface is provided on the base unit 102.

The test current source 332, driven return circuitry 334, and analog todigital converter 336 are parts of the electrode contact qualityevaluation circuitry 120, described in more detail herein. (In someembodiments the driven return circuitry 334 and analog to digitalconverter are shared within the instrument electronics 306.) The testcurrent source 332 generates a test signal that is delivered to one ofthe leads 110 and electrodes 112 that are selected with the injectionelectrode selection circuitry 322. The driven return circuitry 334generates a signal of approximately equal magnitude but of oppositepolarity, which is delivered to another one of the leads 110 andelectrodes 112 that are selected with the return electrode selectioncircuitry 324. The resulting signals are then sensed relative to a thirdone of the leads 110 and electrodes 112 or relative to a selectedaverage of two or three of these that are selected by the senseelectrode selection circuitry 326. The resulting signals are convertedfrom an analog into a digital form by the analog to digital converter336, and processed by the processing device 328.

In most embodiments the test signal generated by the test current source332 is an alternating current (AC) signal. The AC test signal can bedetected independent from the magnitudes of any DC offsets that may bepresent, such that the DC offsets do not impact the readings. In someembodiments, the test current source 332 generates a test signal havinga square wave shape. Other embodiments can use other wave shapes, suchas sinusoidal or triangular wave shapes, but a square wave is simplestto create.

The AC frequency of the test signal is selected according to severalcriteria. One criterion is that the frequency should be within thepassband of the electronic components 242 and/or instrument electronics306. Another criterion is that the frequency must be less than half thesampling frequency of the analog to digital converter 336. In an exampleembodiment, the sampling frequency of the analog to digital conversionis about 1,000 Hz, although other embodiments may have other samplingfrequencies. In some embodiments, it is desirable that the testfrequency be an even sub-multiple of the sampling frequency, such as (¼)or (⅛) of the sampling frequency. Within these guidelines, a higherfrequency will improve the rejection of artifacts. For example,interference generated by a 60 Hz power line will impact the detectedsignal less if the test frequency is much greater than the 60 Hzfrequency. Considering these criteria, some embodiments generate a testsignal having a frequency of 125 Hz or 250 Hz.

The analog to digital converter 336 measures signals that are receivedon the injected and driven return electrodes 112 and corresponding leads110 relative to the electrode that is selected by the sense electrodeselection circuitry 326. In some embodiments one or the average of twoor more electrodes 112 and corresponding leads 110 can be selected atone time by the sense electrode selection circuitry 326, provided thatnone of the AC test current is flowing through the selected sensedelectrodes 112 and leads 110, because such current flow would impact theaccuracy of the results. Instead, it is desired that no current isflowing through any of the one or more electrodes 112 and leads 110 thatare selected by the sense electrode selection circuitry 326.

The signals measured by the analog to digital converter 336 are passedto the processing device 328 for further evaluation. The processingdevice 328 computes the contact impedances of individual electrodesusing the signals detected by the analog to digital converter 336. Thecontact impedances can then be evaluated to determine the quality of thecontact between the individual electrode 112 and the patient P. In someembodiments, the contact impedances for two electrodes can be determinedwith a single test operation.

The base unit interface 338 includes electronics that handlecommunications between the lead interface unit 108 and the base unit 102(FIG. 1). For example, the base unit interface 338 sends datarepresenting the signals generated by the heart of the patient P to thebase unit 102 for further processing. The base unit interface 338 canalso receive commands from the base unit 102, such as to adjust a modeof operation of the lead interface unit 108 based on inputs receivedfrom the user. In some embodiments that include cable 106, the base unitinterface 338 also provides electrical isolation between the base unit102 and the lead interface unit 108.

In some embodiments, the base unit interface 338 is physically andelectrically connected to the cable 106, which carries the communicationsignals between the lead interface unit 108 and the base unit 102. Inother embodiments, the base unit interface 338 includes a wirelesscommunication device that wirelessly communicates with the communicationinterface 144 (FIG. 3) of the base unit 102. Wireless communicationapproaches inherently include electrical isolation.

FIG. 9 is a schematic diagram illustrating an example of the electrodecontact quality evaluation circuitry 120, shown in FIG. 7. FIG. 9 alsoillustrates the connection of the electrode contact quality evaluationcircuitry 120 with the skin S of the patient P through the leads 110 andelectrodes 112.

In this example, the electronic components 242 of the lead interfaceunit 108 (shown in FIG. 8) include protection circuitry 320, andelectrode contact quality evaluation circuitry 120. In this example, theelectrode contact quality evaluation circuitry 120 utilizes at leastsome of the instrument electronics 306, which in this case include ECGacquisition electronics. The electrode contact quality evaluationcircuitry 120 also includes and utilizes the analog to digital converter336 and the processing device 328. The processing device 328 operates toperform processing operations of the electrode contact qualityevaluation circuitry 120 as part of the determination of the quality ofelectrical connections between the electrodes 112 and the patient P, asdescribed in more detail herein. In addition to the specific function ofthe processing device 328 illustrated and described in FIG. 9, theprocessing device 328 also performs control operations in someembodiments to control the operation of the lead interface unit 108electronic components 242.

The schematic in FIG. 9 is simplified to show only three electrodes 112(including electrodes 352, 354, and 356) and three associated leads(including leads 362, 364, and 366). The three leads are selected by theselection circuitry 322, 324, and 326 shown in FIG. 8. For example, aninjection electrode 352 and lead 362 are selected by the injectionelectrode selection circuitry 322 (FIG. 8), which makes contact with theselected lead 362 through circuit point 323 (FIG. 9). The senseelectrode 354 and lead 364 are selected by the sense electrode selectioncircuitry 326, which makes contact with the selected lead 364 throughcircuit point 327. The return electrode 356 and lead 366 are selected bythe return electrode selection circuitry 324, which makes contact withthe selected lead 366 through circuit point 325.

The human body is comprised of a large percentage of water, which makesthe body a good conductor of electricity. When the electrodes 112 areproperly connected to the skin S of the patient's body P, the electrodes112 make an electrical connection with the body, such that electricalsignals can be applied to or detected from the body. Although the bodyis a good conductor of electricity, it still has some impedance. Thisimpedance is represented by Z_(BODY). Typically the impedance of thebody is much lower than other circuit impedances, however, and as aresult the impedance of the patient's body Z_(BODY) can typically beignored and treated as a short circuit amongst the electrodes 112.

When the electrodes 112 are connected to the patient's skin S, a contactimpedance exists at the intersection between the electrodes 112 and thepatient's skin S. For example, the injection electrode 352 has animpedance Z_(I), the sense electrode 354 has an impedance Z_(S), and thereturn electrode has an impedance Z_(R). When proper skin preparationsteps are performed, and proper electrode application procedures arefollowed, the electrode contact impedance will be relatively low (e.g.,less than 10K ohms). When proper skin preparation steps are notperformed, or proper electrode application procedures are not followed,the electrode contact impedance can be an order of magnitude higher, ormore (e.g., greater than 120K ohms). The instrument 100 (shown inFIG. 1) operates most effectively when the contact impedances betweenthe electrodes 112 and the skin S are low. High contact impedances candegrade the quality of the detected signals by enabling the pickup andgeneration of increasing amounts of artifacts along with the desiredsignals.

In addition to the contact impedances, DC offset voltages can accumulateat the electrodes 112. The DC offsets are represented by voltage sourcesVI, VS, and VR, for the injection electrode 352, the sense electrode354, and the return electrode 356, respectively. Due to the possiblepresence of DC offsets on the electrodes 112, in preferred embodimentsthe electrode contact quality evaluation circuitry 120 is configured toproperly determine electrode contact quality regardless of whether ornot such DC offsets are present on the electrodes 112.

The electrodes 112 are each connected to the lead interface unit 108through one or more leads 110. For example, the injection electrode 352is connected to injection lead 362, the sense electrode 354 is connectedto sense lead 364, and the return electrode 356 is connected to returnlead 366. The impedance of the leads 110 is typically negligible and cantherefore be ignored in some embodiments and treated as a short circuit.

The protection circuitry 320 is provided to protect the electroniccomponents 242 from large external electrical signals. For example, if adefibrillation shock is delivered to the patient, the protectioncircuitry operates to protect the electronic components 242 from largecurrents and voltages that may be applied to the electrodes 112. Theprotection circuitry 320 can take various forms in differentembodiments. In this example, the defibrillation protection circuitry isprovided for each lead 110, and comprises a series resistor R_(SERIES)and a clamp circuit 372, 374, and 376, respectively. The resistance ofthe series resistor is selected according to the needs of the particularimplementation, and in view of the external sources that are likely tobe encountered. As one example, R_(SERIES) is about 10K ohms. Examplesof clamp circuits 372, 374, and 376 are described herein.

In this example, the protection circuitry 320 is provided between theinjection current source 332 (circuit point 323) and the lead 362, toprotect the injection current source 332. The protection circuitry alsoincludes passive low pass filter circuitry.

In some embodiments, the electrode contact quality evaluation circuitry120 includes a test current source 332, a driven return 334,differential amplifiers 380 (such as provided by the ECG acquisitionelectronics 306), an analog to digital converter 336, and a processingdevice 328. The following discussion describes an exemplary operation ofthe electrode contact quality evaluation circuitry 120 when theinstrument 100 is operating in an electrode contact quality evaluationmode to perform an electrode contact quality evaluation operation. Inthis example, the contact quality evaluation operation determines thequality of the electrical connections of the injection electrode 352 andthe return electrode 356 in a single operation, by determining thecorresponding contact impedances.

The test current source 332 generates an AC test signal that is injectedinto the injection lead 362 and injection electrode 352 at circuit point323. As discussed herein, the test current source 332 is typically acurrent source that generates an AC signal at a selected frequency, suchas at 125 Hz or 250 Hz, although other frequencies can be used in otherembodiments. The current (I_(TEST)) flows through the protectioncircuitry 320, including the series resistors R_(SERIES) and R_(FILTER),through the injection lead 362, and into the electrode 352.

The electronic components 242 operate to select one or more of theelectrodes 112 as sense electrode 354 and the corresponding one or moreleads 110 as sense lead 364. For example, an average of two or moreelectrodes 112 can be treated as the sense electrode 354. The electroniccomponents 242 operate so that no significant portion of the testcurrent (I_(TEST)) is conducted through the sense electrode 354 and lead364. In this way, no significant current is conducted through thecontact impedance Z_(S), or the series resistors R_(SERIES) andR_(FILTER), so that no significant voltage related to I_(TEST) isdeveloped across any of these latter impedances. In some embodiments,when multiple electrodes 112 are selected as the sense electrode 354,the signal at circuit point 327 can be an average of the signals at eachof the electrodes, which is then provided to the driven return 334.

A driven return 334 is provided in some embodiments to accept the returnof the test current (I_(TEST)) through the return electrode 356 and thereturn lead 366. The driven return 334 is electrically coupled betweenthe sense electrode 354 (at circuit point 327) and the return electrode356 (at circuit point 325) by the sense electrode selection circuitry326 and the return electrode selection circuitry 324 (both shown in FIG.8).

The driven return 334 operates to sink all (or substantially all) of thetest current (I_(TEST)) from the test current source 332 to the returnelectrode 356 and return lead 366. The driven return 334 operates tokeep the voltage at the sense electrode 354 centered at an isolatedground potential for the instrument 100).

In some embodiments, a driven return circuit may also be included withinthe ECG acquisition electronics 306, which is used by the instrument 100during a normal operating mode. If so, the driven return of the ECGacquisition electronics 306 can be used as the driven return 334 forpurposes of the electrode contact impedance evaluation, rather thanincluding separate circuits.

During the test operation, when the test current (I_(TEST)) is beinggenerated by the test current source 332, differential voltages aregenerated. For example, a voltage differential of V_(IS) is generatedbetween the injection circuit point 323 and the sense circuit point 327,and a voltage differential of V_(SR) is generated between the sensecircuit point 327 and the return circuit point 325. Because the testcurrent (I_(TEST)) is an AC signal, only the AC component related toI_(TEST) is evaluated, so that any electrode DC offsets are ignored.This removes the effect of any DC offsets V_(I), V_(S), and V_(R) thatmay be present in the system.

In this example, the ECG acquisition electronics 306 includesdifferential amplifiers 380 which receive the differential voltages andamplify the signals with a predetermined gain (G1). The amplifiedsignals are then measured by the analog to digital converter 336. Thedigital data representing the measured amplified differential voltagesV_(IS) and V_(SR) is then stored in a computer readable storage device,at least temporarily, by the processing device 328. Further processing328 is then performed by the processing device 328.

The differential amplifiers 380 are an example of at least part ofdifferential measurement circuitry. In some embodiments the differentialmeasurement circuitry further includes at least an analog to digitalconverter. Although the gain of these differential amplifiers willtypically be greater than unity, it is also possible to determinecontact quality if their gain is unity.

Once the differential voltages have been determined, the magnitude ofthe contact impedances for the injection electrode 352 and the returnelectrode 356 can be computed by the processing device 328 using Ohm'slaw, because all other variables in the equations are known. Equations 1and 2 illustrate Ohm's law for the differential voltages V_(IS) andV_(SR).

V _(IS)=(V _(I) −V _(S))+I _(TEST)*(R _(SERIES) +R _(FILTER) +Z_(I))  Equation 1:

V _(SR)=(V _(S) −V _(R))+I _(TEST)*(Z _(R) +R _(SERIES) +R_(FILTER))  Equation 2:

Because no test current flows through the sense electrode 354 and thesense lead 364, no voltage drop occurs across the contact impedanceZ_(S) or the associated series resistors, and therefore Equations 1 and2 do not include contributions from these components.

In embodiments in which the differential voltages are amplified, such asby the differential amplifiers 382 and 384 having a gain of G1, thedetected voltages V_(IS) and V_(SR) are multiplied by the known gain(G1), as shown in Equations 3 and 4.

Amplified V _(IS) =G1*((V _(I) −V _(S))+I _(TEST)*(R _(SERIES) +R_(FILTER) +Z _(I)))  Equation 3:

Amplified V _(SR) =G1*((V _(S) −V _(R))+I _(TEST)*(Z _(R) +R _(SERIES)+R _(FILTER)))  Equation 4:

Therefore, amplified V_(IS), amplified V_(SR), G₁, I_(TEST), R_(FILTER),and R_(SERIES) are all known (or measured) values, such that the onlyremaining variables are the DC offsets (V_(I), V_(S), and V_(R)) and thecontact impedances Z_(I) and Z_(R).

The processing device 328 processes the detected V_(IS) and detectedV_(SR) signals. In some embodiments, the processing device 328 performsfull wave synchronous detection to determine the peak to peak values ofthe detected signals. By utilizing the computed peak to peak values, theDC offsets make no net contribution, thereby removing those componentsfrom Equations 3 and 4.

In some embodiments, the processing device 328 further filters thesignal utilizing an integration operation. The integration operationsuccessively adds the detected peak to peak voltages for each period ofthe test signal, which averages out the contributions from externalsources such as power line frequencies, pacemaker pulses, and the like,because such contributions will not be synchronized with the test signalor the sampling frequencies. Further, if a particular sample is muchdifferent than a previous sample (such that it exceeds a predeterminedthreshold difference value), the processing device 328 can operate toskip a full period of the detected signal from the integration operationto reduce the effects of large voltage spikes that may be present (suchas from a pacemaker pulse). Excluding a full period of the test signalrather than just one sample is necessary because peak to peak signalvalues are required. In this case, the test operation is extended for anequivalent duration (an additional full period of the test signal). Thisadditional filtering operation removes the effect of pacemaker pulsesand other potentially large artifacts from the detected results, therebyimproving the accuracy of the contact impedance calculations.

The results can then be used by the processing device 328 to compute thecontact impedances Z_(I) and Z_(R) for the injection electrode 352 andfor the return electrode 356. Therefore, with a single test operation,the contact impedances for two individual electrodes 352 and 356 can besimultaneously measured.

In the above discussion, some approximations are made. For example, itis recognized that impedances may include a real component and animaginary component. Although the above computations could alternativelybe performed utilizing both real and imaginary components, it isadequate to simplify the computations to the real components. Also notethat for purposes of evaluating electrode contact quality, precisemeasurements of impedance are not required.

FIG. 10 illustrates a simplified example of the driven return circuitry334. In this example, the driven return circuitry 334 includes a buffer402 and an inverting amplifier 404. An example of the invertingamplifier includes an op amp 406 and resistors R1 and R2 arranged in aninverting amplifier configuration.

The signal from circuit point 327 (FIG. 9) is provided to the buffer 402and is then inverted and amplified by the inverting amplifier 404. Thegain of the inverting amplifier is set by the ratio of R2 to R1 toobtain the appropriate gain. In some embodiments, the gain is in a rangefrom about 10 to about 100. During testing, the signals obtained fromthe injected electrode are well behaved, and have only small amounts ofpower line frequency interference. However, it is normal when an ECGdevice is used in an electrically-noisy environment for the voltage on adriven reference electrode to contain relatively large amounts of powerline frequency interference. (This is consistent with the way a drivenreference electrode is supposed to work.) Consequently, signals obtainedfrom a reference electrode may be so erratic as to be unusable unlessproper processing is used.

Although the term “driven reference electrode” is sometimes used herein,the driven reference electrode also serves as a return path for theinjected test current. Accordingly, the terms “driven return electrode”and “return electrode” are sometimes alternatively used herein to referto the same electrode which serves all of these functions.

To be usable, signals that are obtained from the driven referenceelectrode must be integrated over longer intervals during thesynchronous detection process than for signals obtained from theinjected electrode. Ideally, the integration interval for signalsobtained from the driven reference electrode should contain wholeperiods of any expected power line frequency—most particularly of both60 Hz and 50 Hz. To meet this latter condition requires usingintegration intervals that are integer multiples of 100 milliseconds.

Although using such integration intervals removes most power linefrequency interference from the integrated measurements, it cannotalways sufficiently reject artifact from implanted pacemakers. Theprocessing technique of excluding samples that deviate from the averageby more than a certain amount works quite well for removing pacemakerpulse artifact from signals obtained from an injected electrode, but agreat percentage of the samples obtained from a driven electrodeinherently deviate excessively from its average. The simplest andperhaps the only effective way of removing pacemaker pulse artifact fromsignals obtained from the driven electrode is averaging over asufficiently long interval, e.g. at least several tenths of a second.

FIG. 11 is a flow chart illustrating an example method 420 of operatingan instrument 100 using surface contact electrodes. In this example,method 420 includes operations 422, 424, 426, 428, 430, 432, 434, 435,436, and 438.

The operation 422 generates a periodic timing tick, in order torepetitively trigger checking for any lead off conditions. The timing ofthese ticks is a compromise between response time for detecting when alead is connected or disconnected versus the processing burden consumedby the testing.

The operation 424 is performed to detect the connection of theelectrodes. While performing the operation 424, the instrument operatesin an electrode connection detection mode. In some embodiments, theoperation 424 is performed by the electrode contact detection circuitry302, shown in FIG. 7.

In some embodiments, a visual indication is presented by the instrument100 to identify those electrodes that are determined to be connected.For example, a light or graphical element is illuminated on the displaydevice 246 of the lead interface unit 108 (FIG. 8), and/or on thedisplay device 132 of the base unit 102 (FIG. 3), as the connection ofeach electrode is detected. This operation 434 provides a visualindication to the user that the instrument 100 has detected theconnection of the electrode or set of electrodes.

The operation 426 is performed to determine whether the electrodes areconnected. In some embodiments, the operation 426 waits for allelectrodes to be connected before proceeding with the subsequentoperations. In other embodiments, the operation 426 waits for at least asubset of the electrodes (e.g., at least three electrodes) to beconnected before proceeding with subsequent operations. In someembodiments, the operation requires only three or more electrodes beconnected in order to proceed to subsequent operations.

In some embodiments, the debounce operation 428 is included to preventunintentional startups of determining contact quality because oftransient behavior of the output state of the operation 426. Forexample, such transients may occur when a patient is defibrillated whileconnected to instrument 100.

In some embodiments, it is desirable to automatically trigger testing ofcontact quality after the last electrode or the last electrode of adefined subset of electrodes is connected to the patient. Furthermore itis desirable in some embodiments to allow the user to manually command arepeat of the contact quality testing when desired e.g., after theelectrodes have been in place for a long time and their contact qualitymay be suspect. Operation 430 provides these control actions.Alternatively, an automatic re-test may be triggered periodically.

Once the appropriate number of electrodes are determined to have beenconnected, the operation 432 is performed to determine the quality ofthe electrode connections. For example, in some embodiments theinstrument 100 determines the contact impedances of each of theconnected electrodes, such as illustrated and described with referenceto FIG. 12. In some embodiments the instrument 100 determines a qualitylevel of the electrode connections, such as illustrated and describedwith reference to FIG. 13. One example of electrode quality levelsinclude “good,” “fair,” and “poor.” Further, in some embodiments theinstrument 100 generates visual indications of the electrode contactquality levels, such as illustrated and described with reference toFIGS. 14 and 15. Still other embodiments use numbers to offer greaterresolution for contact quality, e.g. where 1 is best and 10 is too poorto use.

In some embodiments, a visual indication is presented by the instrument100 to identify the contact quality of those electrodes that aredetermined to be connected. For example, a light or graphical element isilluminated on the display device 246 of the lead interface unit 108(FIG. 8), and/or on the display device 132 of the base unit 102 (FIG.3), as the connection of each electrode is detected. This operation 434provides a visual indication to the user of the contact quality of eachconnected electrode.

The operation 435 is performed to determine if the electrode contactquality level is of sufficient quality. In some embodiments, each of thedetermined electrode contact impedances is compared with a predeterminedmaximum acceptable electrode contact impedance. If any of the determinedelectrode contact impedances exceed the maximum acceptable electrodecontact impedance, the corresponding electrodes are determined to haveinsufficient electrode contact quality.

In another example embodiment, the determined electrode contact qualitylevels are evaluated to determine whether they are of sufficientquality. As one example, electrode contact quality levels of “good” and“fair” are determined to be of sufficient quality, while a contactquality level of “poor” is determined to be of insufficient quality.

If one or more electrodes are determined to have insufficient electrodecontact quality, the operation 436 is performed to generate an alert. Anexample of an alert is a visual indication, such as shown in FIG. 15.Such a visual indication may be displayed on a user interface, such ason the display device 246 of the lead interface unit 108 (FIG. 8),and/or on the display device 132 of the base unit 102 (FIG. 3). Themessage informs the user that at least one of the electrodes is notadequately connected to the patient, and may instruct the user toreconnect one or more of the electrodes, for example. In someembodiments, the alert identifies the one or more electrodes that arenot adequately connected. Another example of an alert is an audiblealert, such as a beep, or other audible sound. Other embodiments utilizeother alerts or combinations of alerts.

In some embodiments, operation 435 inhibits normal instrument operationuntil the quality of the electrode connections are determined to besufficiently high. In another possible embodiment, the instrumentincludes an override mode 437. Upon receiving an input from the userindicating a desire to proceed with instrument operation despite theinsufficient quality of the connection of one or more electrodes, themethod 420 proceeds to the operation 438.

If all electrodes are determined to have sufficient quality or anoverride command 437 is received, the operation 438 is performed toproceed with normal instrument operation. For example, when theinstrument 100 is an ECG instrument, the operation 438 proceeds tomonitor electrical signals from the heart using the electrodes.

FIG. 12 is a flow chart illustrating an example method 440 ofdetermining electrode contact impedances. In some embodiments, themethod 440 is an example of part or all of the operation 432, shown inFIG. 11, which operates to determine the quality of electrodeconnections. In this example, method 440 includes operations 442, 444,446, 448, 450, and 452.

The operation 442 selects at least three electrodes from the completeset of electrodes. In some embodiments, the operation 442 involves theselection of an electrode as an injection electrode, one or the averageof two or more other electrodes as a sense electrode, and a thirdelectrode as a return electrode, where the method 440 is then performedto determine the contact impedances for the electrodes selected as theinjection electrode and the return electrode. In some embodiments, oncethe electrodes have been selected, signals are generated to control theinjection, return, and sense electrode selection circuitry 322, 324, and326 (shown in FIG. 8) to make the appropriate selections.

The operation 444 involves applying a test signal to the injectionelectrode. Examples of the test signal are described herein. In someembodiments, operation 444 is performed by the test current source 332(shown in FIGS. 8 and 9).

The operation 446 generates a return signal of opposite polarity andapplies that signal to the return electrode. In some embodiments,operation 446 is performed by the driven return circuitry 334 (shown inFIGS. 8-10).

The operation 448 determines the voltage drop of the test signal and thereturn signal. In some embodiments, operation 448 involves determiningthe voltage drop between the test current source and the sense electrode354 (FIG. 9). In another embodiment, the voltage drop is thedifferential voltage V_(is) across circuit points 323 and 327 (FIG. 9).

In some embodiments, operation 448 also involves determining the voltagedrop between the driven return circuitry 334 and the sense electrode 354(FIG. 9). In another embodiment, the voltage drop is the differentialvoltage V_(SR) across circuit points 327 and 325 (FIG. 9).

In some embodiments, the differential voltages are amplified prior tomeasurement.

The operation 450 is then performed to compute contact impedances forthe injection electrode and the return electrode using the voltage dropsdetermined in operation 448.

Operation 452 is then performed to repeat the operations 442, 444, 446,448, and 450 with at least one different electrode. The process can berepeated until the contact impedances of all electrodes have beendetermined.

FIG. 13 is a flow chart illustrating an example method 460 ofdetermining an electrode contact quality level. In some embodiments themethod 460 is at least part of the operations 432 or 435, shown in FIG.11. In this example, method 460 includes operations 462, 464, and 466.

The operation 462 is performed to determine electrode contactimpedances. An example of operation 462 is method 440, shown in FIG. 12.

Operation 464 is then performed to compare the electrode contactimpedances with predetermined contact impedance values for variousquality levels. In some embodiments the operation 464 involves lookingup the electrode contact impedance for an electrode in a lookup table.An example of a lookup table is shown in Table 1.

TABLE 1 Electrode Contact Impedance (X) Contact Quality Level X <= 10Kohms Good 10K ohms < X <= 80K ohms Fair 80K ohms < X <= 120K ohms PoorX > 120K ohms Disconnected

Note that contact impedances are to a first order inversely proportionalto the frequency of the test signal. Therefore, the values in a lookuptable that is appropriate for one embodiment may not be appropriate foruse with an embodiment that uses a different test frequency.

The operation 466 is then performed to identify an electrode contactquality level for the electrode. For example, if an electrode contactimpedance is determined to be 8K ohms, Table 1 is used to identify thecontact quality level as “good.” If an electrode contact impedance isdetermined to be 25K ohms, Table 1 is used to identify the contactquality level as “fair.”

FIG. 14 is a flow chart illustrating an example method 480 of generatinga visual indication of the electrode contact quality level. In thisexample, the method 480 includes operations 482 and 484.

After an electrode contact quality level has been determined, such asthrough the method 460, shown in FIG. 13, operation 482 is performed todetermine a color associated with an electrode contact quality level. Insome embodiments, the color is determined from a lookup table, such asthe example shown in Table 2.

TABLE 2 Electrode Contact Quality Level Color Good First Color (Green)Fair Second Color (Yellow) Poor Third Color (Off or Flashing Yellow)Disconnected None

The operation 484 is then performed to generate a visual indication ofthe electrode contact quality level using the color. An example isillustrated in FIG. 15.

FIG. 15 is a diagram illustrating an example display 490 showingelectrode contact quality levels.

In some embodiments, the display 490 is generated by the instrument 100to convey to the user information regarding the determined electrodecontact quality levels for each of the electrodes. In this example, thedisplay 490 includes a graphical representation of a person 492, andgraphical elements 494 representing each of the electrodes. Thegraphical elements 494 include graphical elements 496, 498, 500, 502,504, 506, 508, 510, 512, and 514.

In some embodiments, the display 490 is generated by the display device246 of the lead interface unit 108 (FIG. 8). In another embodiment, thedisplay 490 is generated by the display device 132 of the base unit 102(FIG. 3). In still other embodiments, display 490 may be generated onboth the base unit 102 and the lead interface unit 108.

The graphical representation of the person 492 can be generated anddisplayed on a display device, such as by illuminating pixels on an LCDdisplay or other type of flat panel display. In another embodiment, thegraphical representation can be physically printed, imprinted, molded,or otherwise formed on a housing or other portion of the instrument 100.

The graphical elements 494 convey the electrode contact quality levelfor each electrode to the user, such as by using different colors fordifferent quality levels. In some embodiments the graphical elements 494are generated and displayed on a display device, such as by illuminatingpixels on an LCD or other type of flat panel display. In anotherpossible embodiment, the graphical elements 494 are LED's, such asmulti-color LED's that can be selectively illuminated to generatedifferent colored outputs.

In some embodiments, the graphical elements 494 include only a singlecolor. For example, the graphical element 494 is illuminated when theelectrode contact quality level is sufficient and is off when thequality level is insufficient. As another example, the graphical element494 is illuminated when the electrode contact quality level isinsufficient and is off when the quality level is sufficient.

In other embodiments, the graphical elements 494 include multiplecolors, such as illustrated in FIG. 15. In this example, the graphicalelements 494 include at least three colors. A first color 520 (e.g.,green) represents a good quality level. A second color 522 (e.g.,yellow) represents a fair quality level. A third color 524 (e.g., blackor off) represents a poor quality level. The graphical element 494 beingoff indicates that the electrode is disconnected.

In this example, most of the electrodes have been determined to have agood electrode contact quality level, including the electrodesrepresented by graphical elements 496, 500, 502, 506, 508, 510, and 512,and are therefore displayed with the first color. The electrodesrepresented by graphical elements 504 and 514 were determined to havefair, but lower, quality electrode contact quality levels, and aretherefore displayed with the second color. The electrode represented bygraphical element 498, however, was determined to have a poor electrodecontact quality level, and is therefore displayed with the third color.

Various other visual representations of electrode contact qualitylevels, including the addition of blinking presentation, or of theelectrode contact impedance values themselves, can be provided in otherembodiments.

In addition to conveying information regarding electrode contact qualityto the user, such information can also be stored and/or transmitted forsubsequent use. For example, a log can be maintained identifyingelectrode contact quality levels that were detected, along with the dateand time in which the contact quality evaluation was performed. This canbe helpful, for example, for subsequent troubleshooting and forevaluating the operation of the instrument 100.

The various embodiments described above are provided by way ofillustration only and should not be construed to limit the claimsattached hereto. Those skilled in the art will readily recognize variousmodifications and changes that may be made without following the exampleembodiments and applications illustrated and described herein, andwithout departing from the true spirit and scope of the followingclaims.

What is claimed is:
 1. An instrument comprising: a lead interface deviceconfigured to electrically communicate with at least three surfacecontact electrodes; instrument electronics configured to detectelectrical signals from the surface contact electrodes; and electrodecontact quality evaluation circuitry operable to determine a quality ofelectrical connections between the surface contact electrodes and a skinsurface.
 2. The instrument of claim 1, further comprising: electrodecontact detection circuitry operable to determine whether two or more ofthe surface contact electrodes have been placed on the skin surface;wherein the instrument controls the electrode contact detectioncircuitry and the electrode contact quality evaluation circuitryseparately, so that the electrode contact quality evaluation circuitryoperates after the electrode contact detection circuitry successfullydetects at least three of the surface contact electrodes have beenplaced on the skin surface.
 3. The instrument of claim 1, wherein theelectrode contact quality evaluation circuitry is operable to determinea contact impedance indicative of the quality of the electricalconnection between at least one of the surface contact electrodes andthe skin surface with a single test operation.
 4. The instrument ofclaim 3, wherein the determination of the contact impedance isindependent of a magnitude of a DC offset present in at least one of thesurface contact electrodes.
 5. The instrument of claim 3, wherein theelectrode contact quality evaluation circuitry is operable tosimultaneously determine at least two separate contact impedancesindicative of the respective qualities of the electrical connectionsbetween at least two of the surface contact electrodes and the skinsurface with the single test operation.
 6. The instrument of claim 5,wherein the electrode contact quality evaluation circuitry is operableto complete the single test operation when only three surface contactelectrodes are placed on the skin surface.
 7. The instrument of claim 1,wherein the instrument is an electrocardiograph, and wherein theinstrument electronics include electrocardiograph acquisitionelectronics to receive and detect electrical signals from the heart. 8.The instrument of claim 1, wherein the instrument is selected from thegroup consisting of an electroencephalograph, and an electromyograph. 9.The instrument of claim 1, wherein the lead interface device, theinstrument electronics, and the electrode contact quality evaluationcircuitry are all contained within a single housing.
 10. The instrumentof claim 1, wherein the electrode contact quality evaluation circuitryincludes a processing device, and wherein the processing device performsprocessing as part of determining the quality of electrical connectionsbetween the surface contact electrodes and a skin surface.
 11. Anelectrode contact quality evaluation device configured to evaluate aconnection between at least one electrode and a skin surface, theelectrode contact quality evaluation device comprising: a current sourcethat generates a test current; an injection electrode selection circuitthat supplies the test current to a selected injection electrode througha selected injection lead; a driven return circuit that generates areturn current having opposite polarity to the test current; a returnelectrode selection circuit that supplies the return current to aselected return electrode through a selected return lead; a senseelectrode selection circuit that supplies a signal obtained from one ormore selected sense electrodes through one or more selected sense leads,to the driven return circuit; differential measurement circuitry thatmeasures differences between signals present at the injection lead andthe one or more sense leads and between signals present at the one ormore sense leads and the return lead; and a processing device thatevaluates the differences and generates an output representing a qualityof at least one connection between at least one of the electrodes andthe skin surface.
 12. The electrode contact quality evaluation device ofclaim 11, wherein the driven return circuit generates the return currentthe average of which has a magnitude substantially equal to and ofopposite polarity to the test current.
 13. The electrode contact qualityevaluation device of claim 11, wherein the differential measurementcircuitry comprises at least a pair of differential amplifiers, a firstof the differential amplifiers electrically coupled to the selectedinjection electrode and the one or more selected sense electrodes, and asecond of the differential amplifiers electrically coupled to the one ormore selected sense electrodes and the selected return electrode. 14.The electrode contact quality evaluation device of claim 13, whereinoutputs of the differential amplifiers are converted from analog signalsto digital signals by an analog to digital converter, and wherein thedigital signals are provided to the processing device.
 15. The electrodecontact quality evaluation device of claim 11, wherein the driven returncircuit comprises at least an inverting amplifier and is electricallycoupled between the one or more selected sense electrodes and theselected return electrode.
 16. The electrode contact quality evaluationdevice of claim 11, wherein the current source is a square wavegenerator.
 17. An electrocardiograph comprising: a base unit comprising:a housing; a computing device at least partially contained within thehousing; and an output device at least partially contained within thehousing and configured to output information associated with electricalsignals from the heart of a patient detected by the electrocardiograph;a lead interface unit having a lead interface housing separate from thehousing of the base unit, the lead interface unit comprising: a leadinterface arranged and configured to physically connect the leadinterface unit to electrically conductive leads, wherein the leads areconfigured to be physically connected to surface contact electrodes;electrode contact detection circuitry within the lead interface housingthat detects contact between the surface contact electrodes and thepatient; electrode contact quality evaluation circuitry within the leadinterface housing, wherein the electrode contact quality evaluationcircuitry determines a quality of electrical connections between thesurface contact electrodes and the patient; and instrument electronicswithin the lead interface housing that detect electrical signals fromthe heart of the patient; and a communication interface between the leadinterface unit and the base unit.
 18. The electrocardiograph of claim17, wherein the lead interface unit further comprises a display, thedisplay providing an indication of the qualities of the electricalconnections between the surface contact electrodes and the patient. 19.The electrocardiograph of claim 17, wherein the output device of thebase unit is a display, the display providing an indication of thequalities of the electrical connections between the surface contactelectrodes and the patient.
 20. The electrocardiograph of claim 18,wherein the indication of the qualities of the electrical connectionsare displayed at locations of a representation of the patient usingcolor coded graphical elements, wherein the color coded graphicalelements are displayed with a first color if determined that the qualityis good, a second color if the quality is poor, and a third color if noconnection is detected.
 21. A method of evaluating the quality ofelectrode contact with a skin surface, the method comprising: checkingfor and determining that at least three electrodes are in physicalcontact with a skin surface using electrode contact detection circuitry;and evaluating and determine a quality of an electrical connectionbetween at least one of the electrodes and the skin surface usingelectrode contact quality evaluation circuitry.
 22. The method of claim21, further comprising: inhibiting instrument operations if the qualityof the electrical connection is determined to be insufficient.
 23. Themethod of claim 22, wherein evaluating and determining a quality of anelectrical connection comprises: selecting at least one of theelectrodes as an injection electrode, at least another of the electrodesas a sense electrode, and at least another of the electrodes as a returnelectrode; applying a test signal to the injection electrode; applying areturn signal of opposite polarity to the return electrode; determininga voltage drop of the test signal and of the return signal; andcomputing at least one contact impedance for one of the injectionelectrode or the return electrode.
 24. The method of claim 23, whereinevaluating and determining the quality of the electrical connectioncomprises computing a contact impedance for the injection electrode anda contact impedance for the return electrode with a single testoperation.